RESUMEN
We report the most precise measurements to date of the strong-phase parameters between D^{0} and D[over ¯]^{0} decays to K_{S,L}^{0}π^{+}π^{-} using a sample of 2.93 fb^{-1} of e^{+}e^{-} annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider. Our results provide the key inputs for a binned model-independent determination of the Cabibbo-Kobayashi-Maskawa angle γ/Ï_{3} with B decays. Using our results, the decay model sensitivity to the γ/Ï_{3} measurement is expected to be between 0.7° and 1.2°, approximately a factor of three smaller than that achievable with previous measurements, based on the studies of the simulated data. The improved precision of this work ensures that measurements of γ/Ï_{3} will not be limited by knowledge of strong phases for the next decade. Furthermore, our results provide critical input for other flavor-physics investigations, including charm mixing, other measurements of CP violation, and the measurement of strong-phase parameters for other D-decay modes.
RESUMEN
Using a total of 11.0 fb^{-1} of e^{+}e^{-} collision data with center-of-mass energies between 4.009 and 4.6 GeV and collected with the BESIII detector at BEPCII, we measure fifteen exclusive cross sections and effective form factors for the process e^{+}e^{-}âΞ^{-}Ξ[over ¯]^{+} by means of a single baryon-tag method. After performing a fit to the dressed cross section of e^{+}e^{-}âΞ^{-}Ξ[over ¯]^{+}, no significant ψ(4230) or ψ(4260) resonance is observed in the Ξ^{-}Ξ[over ¯]^{+} final states, and upper limits at the 90% confidence level on Γ_{ee}B for the processes ψ(4230)/ψ(4260)âΞ^{-}Ξ[over ¯]^{+} are determined. In addition, an excited Ξ baryon at 1820 MeV/c^{2} is observed with a statistical significance of 6.2-6.5σ by including the systematic uncertainty, and the mass and width are measured to be M=(1825.5±4.7±4.7) MeV/c^{2} and Γ=(17.0±15.0±7.9) MeV, which confirms the existence of the J^{P}=3/2^{-} state Ξ(1820).
RESUMEN
The process of e^{+}e^{-}âpp[over ¯] is studied at 22 center-of-mass energy points (sqrt[s]) from 2.00 to 3.08 GeV, exploiting 688.5 pb^{-1} of data collected with the BESIII detector operating at the BEPCII collider. The Born cross section (σ_{pp[over ¯]}) of e^{+}e^{-}âpp[over ¯] is measured with the energy-scan technique and it is found to be consistent with previously published data, but with much improved accuracy. In addition, the electromagnetic form-factor ratio (|G_{E}/G_{M}|) and the value of the effective (|G_{eff}|), electric (|G_{E}|), and magnetic (|G_{M}|) form factors are measured by studying the helicity angle of the proton at 16 center-of-mass energy points. |G_{E}/G_{M}| and |G_{M}| are determined with high accuracy, providing uncertainties comparable to data in the spacelike region, and |G_{E}| is measured for the first time. We reach unprecedented accuracy, and precision results in the timelike region provide information to improve our understanding of the proton inner structure and to test theoretical models which depend on nonperturbative quantum chromodynamics.
RESUMEN
Using e^{+}e^{-} annihilation data corresponding to an integrated luminosity of 3.19 fb^{-1} collected at a center-of-mass energy of 4.178 GeV with the BESIII detector, we measure the absolute branching fractions B_{D_{s}^{+}âηe^{+}ν_{e}}=(2.323±0.063_{stat}±0.063_{syst})% and B_{D_{s}^{+}âη^{'}e^{+}ν_{e}}=(0.824±0.073_{stat}±0.027_{syst})% via a tagged analysis technique, where one D_{s} is fully reconstructed in a hadronic mode. Combining these measurements with previous BESIII measurements of B_{D^{+}âη^{(')}e^{+}ν_{e}}, the η-η^{'} mixing angle in the quark flavor basis is determined to be Ï_{P}=(40.1±2.1_{stat}±0.7_{syst})°. From the first measurements of the dynamics of D_{s}^{+}âη^{(')}e^{+}ν_{e} decays, the products of the hadronic form factors f_{+}^{η^{(')}}(0) and the Cabibbo-Kobayashi-Maskawa matrix element |V_{cs}| are determined with different form factor parametrizations. For the two-parameter series expansion, the results are f_{+}^{η}(0)|V_{cs}|=0.4455±0.0053_{stat}±0.0044_{syst} and f_{+}^{η^{'}}(0)|V_{cs}|=0.477±0.049_{stat}±0.011_{syst}.
RESUMEN
The cross section of the process e^{+}e^{-}âπ^{+}D^{0}D^{*-} for center-of-mass energies from 4.05 to 4.60 GeV is measured precisely using data samples collected with the BESIII detector operating at the BEPCII storage ring. Two enhancements are clearly visible in the cross section around 4.23 and 4.40 GeV. Using several models to describe the dressed cross section yields stable parameters for the first enhancement, which has a mass of 4228.6±4.1±6.3 MeV/c^{2} and a width of 77.0±6.8±6.3 MeV, where the first uncertainties are statistical and the second ones are systematic. Our resonant mass is consistent with previous observations of the Y(4220) state and the theoretical prediction of a DD[over ¯]_{1}(2420) molecule. This result is the first observation of Y(4220) associated with an open-charm final state. Fits with three resonance functions with additional Y(4260), Y(4320), Y(4360), ψ(4415), or a new resonance do not show significant contributions from either of these resonances. The second enhancement is not from a single known resonance. It could contain contributions from ψ(4415) and other resonances, and a detailed amplitude analysis is required to better understand this enhancement.
RESUMEN
We present the first amplitude analysis of the decay D_{s}^{+}âπ^{+}π^{0}η. We use an e^{+}e^{-} collision data sample corresponding to an integrated luminosity of 3.19 fb^{-1} collected with the BESIII detector at a center-of-mass energy of 4.178 GeV. We observe for the first time the W-annihilation dominant decays D_{s}^{+}âa_{0}(980)^{+}π^{0} and D_{s}^{+}âa_{0}(980)^{0}π^{+}. We measure the absolute branching fraction B(D_{s}^{+}âa_{0}(980)^{+(0)}π^{0^{(}+)},a_{0}(980)^{+(0)}âπ^{+(0)}η)=(1.46±0.15_{stat}±0.23_{sys})%, which is larger than the branching fractions of other measured pure W-annihilation decays by at least one order of magnitude. In addition, we measure the branching fraction of D_{s}^{+}âπ^{+}π^{0}η with significantly improved precision.
RESUMEN
Using a 3.19 fb^{-1} data sample collected at an e^{+}e^{-} center-of-mass energy of E_{cm}=4.178 GeV with the BESIII detector, we measure the branching fraction of the leptonic decay D_{s}^{+}âµ^{+}ν_{µ} to be B_{D_{s}^{+}âµ^{+}ν_{µ}}=(5.49±0.16_{stat}±0.15_{syst})×10^{-3}. Combining our branching fraction with the masses of the D_{s}^{+} and µ^{+} and the lifetime of the D_{s}^{+}, we determine f_{D_{s}^{+}}|V_{cs}|=246.2±3.6_{stat}±3.5_{syst} MeV. Using the câs quark mixing matrix element |V_{cs}| determined from a global standard model fit, we evaluate the D_{s}^{+} decay constant f_{D_{s}^{+}}=252.9±3.7_{stat}±3.6_{syst} MeV. Alternatively, using the value of f_{D_{s}^{+}} calculated by lattice quantum chromodynamics, we find |V_{cs}|=0.985±0.014_{stat}±0.014_{syst}. These values of B_{D_{s}^{+}âµ^{+}ν_{µ}}, f_{D_{s}^{+}}|V_{cs}|, f_{D_{s}^{+}} and |V_{cs}| are each the most precise results to date.
RESUMEN
Using a data sample corresponding to an integrated luminosity of 2.93 fb^{-1} recorded by the BESIII detector at a center-of-mass energy of 3.773 GeV, we present an analysis of the decays D^{0}âπ^{-}π^{0}e^{+}ν_{e} and D^{+}âπ^{-}π^{+}e^{+}ν_{e}. By performing a partial wave analysis, the π^{+}π^{-} S-wave contribution to D^{+}âπ^{-}π^{+}e^{+}ν_{e} is observed to be (25.7±1.6±1.1)% with a statistical significance greater than 10σ, besides the dominant P-wave contribution. This is the first observation of the S-wave contribution. We measure the branching fractions B(D^{0}âρ^{-}e^{+}ν_{e})=(1.445±0.058±0.039)×10^{-3}, B(D^{+}âρ^{0}e^{+}ν_{e})=(1.860±0.070±0.061)×10^{-3}, and B(D^{+}âf_{0}(500)e^{+}ν_{e},f_{0}(500)âπ^{+}π^{-})=(6.30±0.43±0.32)×10^{-4}. An upper limit of B(D^{+}âf_{0}(980)e^{+}ν_{e},f_{0}(980)âπ^{+}π^{-})<2.8×10^{-5} is set at the 90% confidence level. We also obtain the hadronic form factor ratios of Dâρe^{+}ν_{e} at q^{2}=0 assuming the single-pole dominance parametrization: r_{V}={[V(0)]/[A_{1}(0)]}=1.695±0.083±0.051, r_{2}={[A_{2}(0)]/[A_{1}(0)]}=0.845±0.056±0.039.
RESUMEN
We report on new measurements of Cabibbo-suppressed semileptonic D_{s}^{+} decays using 3.19 fb^{-1} of e^{+}e^{-} annihilation data sample collected at a center-of-mass energy of 4.178 GeV with the BESIII detector at the BEPCII collider. Our results include branching fractions B(D_{s}^{+}âK^{0}e^{+}ν_{e})=[3.25±0.38(stat)±0.16(syst)]×10^{-3} and B(D_{s}^{+}âK^{*0}e^{+}ν_{e})=[2.37±0.26(stat)±0.20(syst)]×10^{-3}, which are much improved relative to previous measurements, and the first measurements of the hadronic form-factor parameters for these decays. For D_{s}^{+}âK^{0}e^{+}ν_{e}, we obtain f_{+}(0)=0.720±0.084(stat)±0.013(syst), and for D_{s}^{+}âK^{*0}e^{+}ν_{e}, we find form-factor ratios r_{V}=V(0)/A_{1}(0)=1.67±0.34(stat)±0.16(syst) and r_{2}=A_{2}(0)/A_{1}(0)=0.77±0.28(stat)±0.07(syst).
RESUMEN
Using e^{+}e^{-} annihilation data of 2.93 fb^{-1} collected at center-of-mass energy sqrt[s]=3.773 GeV with the BESIII detector, we measure the absolute branching fraction of D^{0}âK^{-}µ^{+}ν_{µ} with significantly improved precision: B_{D^{0}âK^{-}µ^{+}ν_{µ}}=(3.413±0.019_{stat}±0.035_{syst})%. Combining with our previous measurement of B_{D^{0}âK^{-}e^{+}ν_{e}}, the ratio of the two branching fractions is determined to be B_{D^{0}âK^{-}µ^{+}ν_{µ}}/B_{D^{0}âK^{-}e^{+}ν_{e}}=0.974±0.007_{stat}±0.012_{syst}, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. A study of the ratio of the two branching fractions in different four-momentum transfer regions is also performed, and no evidence for lepton flavor universality violation is found with current statistics. Taking inputs from global fit in the standard model and lattice quantum chromodynamics separately, we determine f_{+}^{K}(0)=0.7327±0.0039_{stat}±0.0030_{syst} and |V_{cs}|=0.955±0.005_{stat}±0.004_{syst}±0.024_{LQCD}.
RESUMEN
We study the e^{+}e^{-}âγωJ/ψ process using 11.6 fb^{-1} e^{+}e^{-} annihilation data taken at center-of-mass energies from sqrt[s]=4.008 GeV to 4.600 GeV with the BESIII detector at the BEPCII storage ring. The X(3872) resonance is observed for the first time in the ωJ/ψ system with a significance of more than 5σ. The relative decay ratio of X(3872)âωJ/ψ and π^{+}π^{-}J/ψ is measured to be R=1.6_{-0.3}^{+0.4}±0.2, where the first uncertainty is statistical and the second systematic (the same hereafter). The sqrt[s]-dependent cross section of e^{+}e^{-}âγX(3872) is also measured and investigated, and it can be described by a single Breit-Wigner resonance, referred to as the Y(4200), with a mass of 4200.6_{-13.3}^{+7.9}±3.0 MeV/c^{2} and a width of 115_{-26}^{+38}±12 MeV. In addition, to describe the ωJ/ψ mass distribution above 3.9 GeV/c^{2}, we need at least one additional Breit-Wigner resonance, labeled as X(3915), in the fit. The mass and width of the X(3915) are determined. The resonant parameters of the X(3915) agree with those of the Y(3940) in BâKωJ/ψ and of the X(3915) in γγâωJ/ψ observed by the Belle and BABAR experiments within errors.
RESUMEN
Using a total of 9.0 fb^{-1} of e^{+}e^{-} collision data with center-of-mass energies between 4.15 and 4.30 GeV collected by the BESIII detector, we search for the processes e^{+}e^{-}âγX(3872) with X(3872)âπ^{0}χ_{cJ} for J=0, 1, 2. We report the first observation of X(3872)âπ^{0}χ_{c1}, a new decay mode of the X(3872), with a statistical significance of more than 5σ for all systematic fit variations. Normalizing to the previously established process e^{+}e^{-}âγX(3872) with X(3872)âπ^{+}π^{-}J/ψ, we find B(X(3872)âπ^{0}χ_{c1})/B(X(3872)âπ^{+}π^{-}J/ψ)=0.88_{-0.27}^{+0.33}±0.10, where the first error is statistical and the second is systematic. We set 90% confidence level upper limits on the corresponding ratios for the decays to π^{0}χ_{c0} and π^{0}χ_{c2} of 19 and 1.1, respectively.
RESUMEN
Based on a sample of (1310.6±7.0)×10^{6}J/ψ events collected with the BESIII detector, we present measurements of J/ψ and η^{'} absolute branching fractions using the process J/ψâγη^{'}. By analyzing events where the radiative photon converts into an e^{+}e^{-} pair, the branching fraction for J/ψâγη^{'} is measured to be (5.27±0.03±0.05)×10^{-3}. The absolute branching fractions of the five dominant decay channels of the η^{'} are then measured for the first time and are determined to be B(η^{'}âγπ^{+}π^{-})=(29.90±0.03±0.55)%, B(η^{'}âηπ^{+}π^{-})=(41.24±0.08±1.24)%, B(η^{'}âηπ^{0}π^{0})=(21.36±0.10±0.92)%, B(η^{'}âγω)=(2.489±0.018±0.074)%, and B(η^{'}âγγ)=(2.331±0.012±0.035)%, where the first uncertainties are statistical and the second systematic.
RESUMEN
By analyzing a 2.93 fb^{-1} data sample of e^{+}e^{-} collisions, recorded at a center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we report the first observation of the semileptonic D^{+} transition into the axial-vector meson D^{+}âK[over ¯]_{1}(1270)^{0}e^{+}ν_{e} with a statistical significance greater than 10σ. Its decay branching fraction is determined to be B[D^{+}âK[over ¯]_{1}(1270)^{0}e^{+}ν_{e}]=(2.30±0.26_{-0.21}^{+0.18}±0.25)×10^{-3}, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of K[over ¯]_{1}(1270)^{0}âK^{-}π^{+}π^{0}.
RESUMEN
The exclusive process e^{+}e^{-}âΛΛ[over ¯], with Λâpπ^{-} and Λ[over ¯]âp[over ¯]π^{+}, has been studied at sqrt[s]=2.396 GeV for measurement of the timelike Λ electric and magnetic form factors, G_{E} and G_{M}. A data sample, corresponding to an integrated luminosity of 66.9 pb^{-1}, was collected with the BESIII detector for this purpose. A multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio R=|G_{E}/G_{M}| and, for the first time for any baryon, the relative phase ΔΦ=Φ_{E}-Φ_{M}. The resulting values are R=0.96±0.14(stat)±0.02(syst) and ΔΦ=37°±12°(stat)±6°(syst), respectively. These are obtained using the recently established and most precise value of the asymmetry parameter α_{Λ}=0.750±0.010 measured by BESIII. In addition, the cross section is measured with unprecedented precision to be σ=118.7±5.3(stat)±5.1(syst) pb, which corresponds to an effective form factor of |G|=0.123±0.003(stat)±0.003(syst). The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon timelike electromagnetic form factors.
RESUMEN
We report the first observation of D^{+}âτ^{+}ν_{τ} with a significance of 5.1σ. We measure B(D^{+}âτ^{+}ν_{τ})=(1.20±0.24_{stat}±0.12_{syst})×10^{-3}. Taking the world average B(D^{+}âµ^{+}ν_{µ})=(3.74±0.17)×10^{-4}, we obtain R_{τ/µ}=Γ(D^{+}âτ^{+}ν_{τ})/Γ(D^{+}âµ^{+}ν_{µ})=3.21±0.64_{stat}±0.43_{syst}., which is consistent with the standard model expectation of lepton flavor universality. Using external inputs, our results give values for the D^{+} decay constant f_{D^{+}} and the Cabibbo-Kobayashi-Maskawa matrix element |V_{cd}| that are consistent with, but less precise than, other determinations.
RESUMEN
Based on an e^{+}e^{-} collision data sample corresponding to an integrated luminosity of 567 pb^{-1} taken at the center-of-mass energy of sqrt[s]=4.6 GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive decay Λ_{c}^{+}âΛ+X to be B(Λ_{c}^{+}âΛ+X)=(38.2_{-2.2}^{+2.8}±0.9)% using the double-tag method, where X refers to any possible final state particles. In addition, we search for direct CP violation in the charge asymmetry of this inclusive decay for the first time, and obtain A_{CP}≡[B(Λ_{c}^{+}âΛ+X)-B(Λ[over ¯]_{c}^{-}âΛ[over ¯]+X)]/[B(Λ_{c}^{+}âΛ+X)+B(Λ[over ¯]_{c}^{-}âΛ[over ¯]+X)]=(2.1_{-6.6}^{+7.0}±1.6)%, a statistically limited result with no evidence of CP violation.
RESUMEN
We report the first observation of a_{0}^{0}(980)-f_{0}(980) mixing in the decays of J/ψâÏf_{0}(980)âÏa_{0}^{0}(980)âÏηπ^{0} and χ_{c1}âa_{0}^{0}(980)π^{0}âf_{0}(980)π^{0}âπ^{+}π^{-}π^{0}, using data samples of 1.31×10^{9} J/ψ events and 4.48×10^{8} ψ(3686) events accumulated with the BESIII detector. The signals of f_{0}(980)âa_{0}^{0}(980) and a_{0}^{0}(980)âf_{0}(980) mixing are observed at levels of statistical significance of 7.4σ and 5.5σ, respectively. The corresponding branching fractions and mixing intensities are measured and the constraint regions on the coupling constants, g_{a_{0}K^{+}K^{-}} and g_{f_{0}K^{+}K^{-}}, are estimated. The results improve the understanding of the nature of a_{0}^{0}(980) and f_{0}(980).
RESUMEN
Using a data sample of e^{+}e^{-} collisions corresponding to an integrated luminosity of 567 pb^{-1} collected at a center-of-mass energy of sqrt[s]=4.6 GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive semileptonic Λ_{c}^{+} decay with a double-tag method. We obtain B(Λ_{c}^{+}âXe^{+}ν_{e})=(3.95±0.34±0.09)%, where the first uncertainty is statistical and the second systematic. Using the known Λ_{c}^{+} lifetime and the charge-averaged semileptonic decay width of nonstrange charmed mesons (D^{0} and D^{+}), we obtain the ratio of the inclusive semileptonic decay widths Γ(Λ_{c}^{+}âXe^{+}ν_{e})/Γ[over ¯](DâXe^{+}ν_{e})=1.26±0.12.
RESUMEN
The cross section of the e^{+}e^{-}âΛ_{c}^{+}Λ[over ¯]_{c}^{-} process is measured with unprecedented precision using data collected with the BESIII detector at sqrt[s]=4574.5, 4580.0, 4590.0 and 4599.5 MeV. The nonzero cross section near the Λ_{c}^{+}Λ[over ¯]_{c}^{-} production threshold is cleared. At center-of-mass energies sqrt[s]=4574.5 and 4599.5 MeV, the higher statistics data enable us to measure the Λ_{c} polar angle distributions. From these, the Λ_{c} electric over magnetic form-factor ratios (|G_{E}/G_{M}|) are measured for the first time. They are found to be 1.14±0.14±0.07 and 1.23±0.05±0.03, respectively, where the first uncertainties are statistical and the second are systematic.